This invention relates to a process for the preparation of N,N-disubstituted mono- and oligourethanes by the reaction of N-aromatically, N-aliphatically, N-cycloaliphatically, and N-araliphatically substituted mono- and oligourethanes with dialkyl carbonates in the presence of at least stoichiometrically equivalent quantities of solid alkali or alkaline-earth carbonate (particularly potassium and/or sodium carbonate) in excess dialkyl carbonate and/or a suitable solvent and in the presence of a phase transfer catalyst.
It is known that monourethanes can be reacted with lower alkyl halides or alkyl sulfates to form N,N-disubstituted monourethanes. See U. Petersen in Houben-Weyl, Volume E4, page 169, edited by Hagemann. However, a disadvantage of the known processes is that good yields are obtained only when special, relatively expensive bases such as metal hydrides (for example, sodium hydride) are used. In addition, because the secondary reaction of olefin formation predominates under these reaction conditions when secondary alkylating agents are used, these processes are limited to the use of primary alkylating agents.
It is also known that N-aryl substituted monourethanes can be N-alkylated with alkyl halides or dialkyl sulfates under the conditions used for phase transfer catalysis. The method fails completely, however, where N-aliphatically substituted urethanes are used. See S. Julia and A. Ginebreda, Anales de Ouimica (Madrid), 75, 346-348 (1979) at page 348, lines 7-13.
In addition, German Offenlegungsschrift 3,609,813 describes a process for the preparation of N,N-disubstituted mono- and oligourethanes in which N-aliphatically, N-cycloaliphatically, and N-araliphatically substituted mono- and oligourethanes are reacted with alkylating agents in the presence of at least stoichiometric quantities of a solid metal hydroxide (in either the presence or absence of an aprotic organic solvent) and optionally in the presence of a phase transfer catalyst.
One common feature of all known processes is that, ultimately, the alkylations are carried out with alkylating agents, almost all of which are known to be physiologically objectionable. For example, N-alkylations are carried out with dimethyl sulfate or methyl chloride or iodide.
An object of the present invention was to provide an economic process for the alkylation of N-aromatically or N-aliphatically substituted urethanes which avoids the disadvantages described above. It has now surprisingly been found that the desired N,N-disubstituted mono- and oligourethanes can be obtained when N-aromatically, N-aliphatically, N-cycloaliphatically, and N-araliphatically substituted mono- and oligourethanes are reacted with dialkyl carbonates in the presence of at least equivalent quantities of solid alkali or alkaline earth carbonate.